Tubing for transporting air samples in an air monitoring system

ABSTRACT

An air monitoring system includes a tubing having a metallic inner layer and an outer jacket to provide optimal transport of air samples.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of U.S. patent applicationSer. No. 10/948,767 filed on Sep. 23, 2004, which application is herebyincorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

The present invention relates generally to air sampling and, moreparticularly, to systems for measuring air characteristics.

BACKGROUND OF THE INVENTION

As is known in the art, there are various applications where air istransported through a tube or pipe for sampling or measurement purposes.For example, an air quality measure system may have remotely locatedsensors instead of at the sensed environment. In addition, a sensor maybe used to sense several locations. For such systems, multiple tubes maybe used to bring air samples from multiple locations to a centralizedsensor(s). Centrally located air switches and/or solenoid valves may beused in these approaches to sequentially switch the air from theselocations through the different tubes to the sensor to measure the airfrom multiple remote locations. These octopus-like or star-configuredsystems use considerable amounts of tubing. Another multiple-locationsampling system known as a networked air sampling system uses a central‘backbone’ tube with branches extending to various locations. Airsolenoids can be remotely located proximate the multiple samplinglocations. Air sampling systems can include remote and/ormultiple-location air sampling through a tube or pipe for samplinglocations in a building, outdoor air or ambient sampling, and samplingin smokestacks and exhaust air stacks. An exemplary air sampling systemis described in U.S. Pat. No. 6,125,710, which is incorporated herein byreference.

As known in the art, air sampling systems can use various types oftubing to transmit air samples or ‘packets’ to the appropriate sensor.One type of tubing is TEFLON tubing. However, TEFLON tubing isrelatively expensive and has certain undesirable particle transportcharacteristics, such that it is a poor conductor and tends to establisha charge as an air sample passes through a tube of such materialresulting in enhanced electrostatic deposition of particulate matterfrom the flow stream. Low or High Density Polyethylene (LDPE or HDPE)tubing, which is less expensive than TEFLON tubing, has been used withlimited success. Although good for indoor air quality CO2 sensing, theLDPE or HDPE tubing absorbs and desorbs volatile organic compounds(VOCs) leading to inaccurate sensing results, This type of tubing isalso poor for particle sensing applications since the plastic is anelectrically poor conductor and can hold a charge resulting inrelatively poor transport properties as a result of electrostaticdeposition.

Some types of plastic tubing can be used for transporting particles. Forexample, one type of plastic tubing is known as “Bev-A-Line XX ” tubingmade by Thermoplastic Processes, Inc. of Stirling, N.J. can be used toperform air sampling with particle transport efficiencies that are animprovement over that possible with polyethylene tubing. However,“Bev-A-Line XX” tubing is quite expensive and absorbs VOCs.

While certain metal tubing may have desirable properties fortransporting air samples, known metal tubing options may have certaindrawbacks. For example, some metal tubing is rigid rendering it quiteexpensive to install, because of the labor involved with that process.While other metal tubing may be deformable so as to facilitateinstallation, the metal characteristics are not well suited for airsampling applications. One known tubing manufactured by Synflex ofMantua Ohio, a division of Saint-Gobain Performance Plastics, includesan aluminum-lined polyethylene tube (Type 1300 Synflex) to provide astronger plastic tube with a higher burst resistance and pressure ratingfor high pressure pneumatic applications. The internal aluminum liner isalso coated with an adhesive to help attach the aluminum inner tubetogether with the outer plastic jacket. It also has a plastic coating onthe inner portion of the tube for added chemical resistance. However,such a tubing configuration is undesirable for use as an air-samplingmedium. The inner coating attracts and traps particles and absorbs VOCs.In addition, even if the coating was not used the aluminum is reactivewith many indoor contaminants. Due to its reactive nature, the aluminumtubing would not give accurate and reliable performance as an airsampling tubing. Further, the aluminum surface has an affinity tooxidize over time as it is exposed to ambient air conditions. Thesurface oxidation increases the roughness of the inside of the tube andcan result in the release of particulate matter in the form of aluminumoxide, which can have a non-negligible impact on a given concentrationof particulate matter being sampled via transport through the tubing.

SUMMARY OF THE INVENTION

The present invention provides a tubing structure that is well suitedfor transporting air samples in an air monitoring system. In anexemplary embodiment, the tubing includes a metallic layer, which can beprovided as stainless steel, to efficiently transport particulate matterwith minimal absorption and off-gassing. The tubing can include a jacketsuch that the overall tubing structure can be bent, cut, and joined in amanner tat is similar to that of conventional tubing.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a block diagram of an air sampling system having tubing inaccordance with the present invention;

FIG. 1A is a block diagram showing further details of the system of FIG.1;

FIG. 2 is a schematic representation of composite tubing in accordancewith the present invention;

FIG. 2A is a schematic depiction of composite tubing having bendingflexibility;

FIG. 3A is a schematic representation of a further embodiment of acomposite tubing in accordance with the present invention;

FIG. 3B is a cross-sectional view of an embodiment of a composite linerthat may be used to line the tubing of FIG. 3A.

FIG. 4 is a schematic representation of another embodiment of acomposite tubing in accordance with the present invention;

FIG. 5A is a width cross-sectional view of another embodiment of acomposite tubing in accordance with the present invention;

FIG. 5B is a length cross-sectional view of the tubing of FIG. 5A;

FIG. 6A is a cross-sectional view of a structured cable assemblyincluding a composite tubing in accordance with the present invention;

FIG. 6B is an isometric view of the structured cable assembly of FIG.6A.

FIG. 7 is a block diagram of an air sampling system having compositetubing in accordance with the present invention;

FIG. 8 is a schematic that illustrates an embodiment of a subsystem thatcan be applied to the system of FIG. 7 to optimize its performance;

FIG. 9 is a cross-sectional view of a structured cable assemblyincluding a resistive conductor;

FIG. 10A is a schematic depiction of the tubing in an air monitoringsystem;

FIG. 10B is a schematic depiction of a tubing joined to a valve within anode controller;

FIG. 10C is a schematic depiction of a tubing joined to a valve thatincludes a shorting strap within a node controller;

FIG. 11 is a cross-sectional view of a tubing that can be used in an airmonitoring system;

FIG. 12 is a schematic depiction showing an ionization source applied toan airflow stream in conjunction with tubing; and

FIG. 13 is a schematic depiction of a multi-point air sampling system.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an exemplary air monitoring system 100 having tubing inaccordance with the present invention to provide optimal transport ofair samples. In general, the system 100 transports air samples orpackets from a first location, such as a room, to a second location atwhich one or more sensors are located. The sensors measure variouscharacteristics of the air, such as CO, CO2, TVOCs, a count per unit ofsample volume of small particles ranging from about 0.3 uM to about 2.5uM, and a count per unit of sample volume of large particles rangingfrom 2.5 uM to 10 uM. The inventive tubing includes a metallic innerlayer and an optional jacket layer. The metallic inner layer, which canbe formed from stainless steel, provides efficient transport ofparticulate matter in the air samples with relatively low absorption andoff-gassing for accurate air quality monitoring.

Before describing the inventive composite tubing in detail, an exemplaryair sampling system as described in U.S. Pat. No. 6,125,710 is brieflydiscussed in which the tubing can be used. The system 100 of FIG. 1includes a central sensing and control system 101 connected to aplurality of air intake valves 103 a-103 d through a network ofcomposite tubing 105. The network of tubing 105 has a backbone section105 e and branches 105 a-105 d corresponding to and connected torespective air intake valves 103 a-103 d. The central sensing andcontrol system 101 includes a sensor suite 107 connected to an end oftubing backbone section 105 e, an air pump 109 connected to the sensorsuite 107 to draw air through the system, and a control andcommunications unit 111 for controlling operation of the sensor suite107, the air intake valves 103 a-103 d, and the air pump 109, as well ascommunicating with the sensor suite 107 and external equipment. Thecontrol and communications unit 111 can control the various elementsthrough a fiber optic, electronic or pneumatic control network 113,including network device adapters 115 (FIG. 1A) for input/outputfunctions and, optionally, a number of control network routers 117 forcontrolling communication within the control network.

Alternatively, the network device adapters 115 and control networkrouters 117 of FIG. 1A can be omitted, with the control andcommunications unit 111 either communicating directly with the deviceadapters 115 or directly with the controlled elements, such as valves103. A digital communications network can be employed as part of thecontrol network 113.

While the air pump 109 draws air through the system, the control andcommunications unit 111 operates the air intake valves 103 a-103 d in asequence, so that each valve (e.g. valve 103 a) is open for a time whilethe others (e.g. valves 103 b-103 d) are closed, thus drawing an airsample into the system from a sample site at which the open valve (e.g.valve 103 a) is located. In the configuration of FIG. 1, air samplesfrom a plurality of valves (e. g., 103 a-103 d) are drawn in the controlsensing and control system 101 through a single backbone section 105 e.Sensor suite 107 thus has only one inlet port to which backbone sectionof tubing 105 e is connected.

The sensor suite 107 measures various parameters of the air samplepassing through the sensor suite. Individual sensors within the sensorsuite 107 may be arranged to receive air from the inlet either in seriesor in parallel, depending upon the flow rate requirements, pressurerequirements and effects of the sensors on the sample chemistry or otherproperties. In a series connection, the air sample passes through eachseries-connected sensor in sequence, while in a parallel connection theair sample passes through each parallel-connected sensor at the sametime. The control and communications unit 111 reads the measurementsmade by the sensor suite 107 and communicates the readings to externalequipment (not shown) such as building air flow controls, fume hoodcontrollers, etc. Either the control and communications unit 111 or theexternal equipment may use the data collected in a variety of ways,including, but not limited to passive data collecting, activating alarmmechanisms under specified conditions, activating safety mechanismsunder specified conditions, and changing local or overall air flowparameters by issuing commands to the air flow control equipment.

According to a first technique, each air intake valve 103 a-103 d isopened in a sequence 103 d→103 c→103 b→103 a, drawing four correspondingsamples D, C, B and A into the sensor unit 107. The time and duration ofopening each valve is selected to be long enough for a stable samplelarger than the inter-sample interface volume to be obtained through theair intake valve 103 a-103 d, thus ensuring a good sample reaching thesensor unit 107 regardless of whether there is a next upstream airintake valve 103 a-103 d to be opened in the sequence. The time forsample A to travel from air intake valve 103 a to the sensor unit 107,TA, is assumed to be known, for example by prior measurement. When thetime TA has passed from the opening of air intake valve 103 a, plus anadditional time necessary to move the portion of the sample A in thesensor unit 107 beyond any interface volume between the sample A and anadjacent prior sample, then the sensor unit 107 performs themeasurements for which it is equipped.

According to a second technique, each air intake valve 103 a-103 d isopened in a sequence 103 a→103 b→103 c→103 d, drawing four correspondingsamples A, B, C and D into the sensor unit 107. Also as described above,each valve is held open for a time sufficient for a stable sample to bedrawn past the next downstream air intake valve to be opened in thesequence or, as is the case for valve 103 d a time sufficient for astable sample to be delivered to sensor unit 107, following which 103 dwill be closed and valve 103 a will be opened to start the sequence overagain. The time is again selected to be sufficient for a stable sample,larger than the inter-sample interface volume, to be obtained throughthe air intake valve 103 a-103 d, thus ensuring a good sample reachingthe sensor unit 107 regardless of whether there is a next downstream airintake valve 103 a-103 d to be opened in the sequence. As above,measurements may be timed to occur at times defined by the known traveltimes TA-TD after each valve 103 a-103 d has opened and the interfacevolume transit time through the sensor unit 107.

Instead of timing, a third technique relies on measuring the samples A-Dwhich are large enough to produce stable measurements over a substantialperiod of time ranging from a few milliseconds to a few seconds. Thesensor unit 107 is continually operated and monitored to determine thedynamic characteristics of the air stream flowing past the sensorscontained therein. During times when the measurements are changing, theinter-sample interface is passing through the sensor unit 107. Duringtimes when the measurements are substantially stable, the useful stableportion of a sample is passing through the sensor unit 107. The sensorunit 107 may be connected to a control system 111 that uses pastmeasurement data to estimate when each future sample will be valid.

FIG. 1A shows further aspects of an air monitoring system, such as thesystem 100 of FIG. 1. The system 100 includes the central sensing andcontrol unit 101, as described in above, connected through tubingnetwork 105 to a plurality of air intake valves 103, as now described.Several subnetworks are defined by backbone sections 105 f-105 k eachconnected to a main backbone including segments 105 e-105 n of tubingnetwork 105 through routers 201. The routers 201 are air flow switches,for example, controlled electronically or pneumatically by control andcommunication unit 111 of the central sensing and control unit 101.

The system 100 can include distributed sourcing/sensing packages 203,connected to at least some branches (e.g. 105 a-105 c) of tubing 105.The distributed sourcing/sensing packages 203 may include one or moresensors and an air pump connected to draw air from the branch of tubing105, through the sensors.

The system 100 provides significant flexibility and redundancy. Byselectively setting the connections made by each of the routers 201 andby selectively opening one of the air intake valves 103, an air samplemay be routed from any air intake valve 103 site to any sensor 101 or203.

The present invention provides a tubing structure having an innermetallic layer, e.g., stainless steel, and an outer jacket that iscomposed at least in part of a non-metallic material, e.g., PVC, foroptimal air transport that is useful in air sampling systems, such asthe system described above, as well as other applications. Non-metallicmaterials may include either synthetic or non-synthetic materials. Theinventive tubing is well suited for air sampling systems that pull airthrough a tube to measure the parameters of the air at a remotelocation. In general, the tubing includes an inner stainless steel linerand an optional outer plastic jacket.

In one embodiment, the tubing has certain mechanical properties that maybe similar to conventional plastic tubing. For example, the inventivetubing can be installed throughout a structure with relative ease as thetubing can be pulled, bent, cut, joined, and otherwise manipulated. Theinstalled cost of the inventive tubing is less than rigid stainlesssteel tube sections and coiled stainless steel tubing. In addition, dueto the relatively low mass and greater flexibility of the tubing inrelation to solid 304 stainless steel tubing, lighter duty fittings canbe used to splice sections together during installation. Thus, lowercost quick-connect fittings, such as the John Guest Super Speedfit®, canbe used. This is desirable over the use of relatively expensiveSwagelok® type fittings, field threaded couplings, and welds, which aretypically required to connect solid stainless steel pipe in order toprovide a reliable connection.

FIG. 2 shows an exemplary composite tubing arrangement 200 including ametallic liner 202 covered by a jacket 204 of suitable material, whichcan be extruded over the liner. In an exemplary embodiment, the liner202 is constructed of a ribbon of stainless steel that has been foldedinto a tubular form and the jacket is made of polyethylene. To improveadhesion of the stainless steel to the plastic jacket an optionaladhesive material, such as an ethylene copolymer or similar preferablyheat-set material, may be used on the outer surface of the metallicliner 202 such that none of the adhesive is material is present on theinside surface of the liner.

In one particular embodiment, the inner liner 202 is formed from 304stainless steel to provide optimal properties for transporting mostgaseous components (including VOCs) and particulate matter at theconcentrations of interest for indoor air quality and other monitoringpurposes. For example, the inventive tubing is suitable for transportingsamples of various gases common within building environments havingconcentrations as low as several parts per billion (PPB). This isespecially useful for monitoring substances which have low permissibleexposure limits (PELs), such as Benzene, Arsine, Chlorine Dioxide, andmost other substances listed, for example, under OSHA RegulationsStandard 29 CFR, which is incorporated herein by reference. Furtherdetails of measuring air contaminants such as these are set forth inU.S. Pat. No. 6,609,967, which is incorporated herein by reference,describing the use of a multi-point sampling system to continuouslymonitor and validate air that is re-circulated from multiple locationswithin a building. The inventive tubing is particularly well suited forlaboratory environments, such as wet chemistry labs, where any varietyof potential contaminants may be present.

As is well known in the art, 304 stainless steel refers to a particularChromium-Nickel austenitic alloy that is one of the most familiar andfrequently used alloys in the stainless steel family. The metallic liner202 is electrically conductive so as to prevent the accumulation ofelectrostatic charge on the inner surface, which helps to promote theefficient transport of particulate matter through the tube for airquality monitoring purposes. The metallic liner 202 also provides aninterior surface having relatively low absorption and off-gassingproperties.

It is understood that the metallic material used for the liner 202 canbe selected based upon its properties with regards to the materials tobe sampled through the tube for a particular application. Exemplaryliner materials include various stainless steels including variousaustenitic, martensitic, and Ferritic grades, along withprecipitation-hardened steels. In one particular embodiment, 304stainless steel is used because of its corrosion and heat resistanceproperties and its good mechanical properties over a wide range oftemperatures. In addition, other suitable metals (depending on theprocess used to form the liner) include but are not limited to bronze,gold, nickel, nickel alloys, titanium alloys, and electricallyconductive conversion coated metals such as aluminum with a chromatecoating.

In an exemplary embodiment, the jacket 204 is provided as polyethylenedue to its ability to provide excellent crush resistance to the metalliner. However, other suitable materials include, but are not limitedto, PVC (particularly one that is suitable for use in plenumenvironments, where that is a requirement), Teflon®, Mylar®, and variousfluoroplastics (FEP, PFA, CTFE, ECTFE, ETFE). More generally, a broadvariety of plastics may be used for the jacket material, based on theworkability, weight, abrasion resistance, stiffness, and smoke and firerating that is desired.

The composite tubing having a metallic liner 202 and plastic jacket 204can be fabricated in a variety of ways using suitable materials. In theexemplary tubing 200 embodiment of FIG. 2, a stainless steel ribbon isformed into a tube with its edges overlapped in a first region 208without any welding. The outer jacket 204, which can be formed frompolyethylene, is then extruded over the stainless steel tube.

Alternatively, a stainless steel ribbon or tape is formed into a tubewith the edges butted together and not overlapped. The seam of thestainless steel ribbon is continuously welded and the polyethylene outerjacket is extruded over it.

In one particular embodiment, the liner 202 is formed from 304 stainlesssteel ribbon having a thickness of 0.002 inch and a width of 1.0 inch.Depending on the parameters of the extrusion process involved in formingthe outer jacket over the stainless steel liner, the stainless steel canbe of any practical thickness ranging from, but not limited to, about0.0005 inch to about 0.004 inch. In an illustrative embodiment, theouter diameter of the tube 200 is about ⅜ inch with an inner diameter of¼ inch to 5/16 inch.

It is understood that various combinations of liner and jacket materialscan be used to meet the needs of a particular application. For example,stainless steel may not be ideally suited for sampling halogenatedhydrocarbons (such as ethylene dichloride, vinyl chloride, and ethylenedibromide), and other halogenated VOCs. These compounds used to be quitecommon in pesticides (e.g. chlordane and heptachlor), cleaning fluids(e.g. carbon tetrachloride), degreasers and paint solvents. The use ofthese compounds has been banned or discouraged in the United Statesbecause of their toxicity, so they are not found in indoor air as oftenas previously. However, they may still be present because old stocksmight still be available and they may also still be in use in foreigncountries. Where there is special interest in measuring this class ofVOCs, the metallic liner 202 may be made of Gold, for example, as Goldis relatively chemically inert for these gaseous components. It isunderstood that the liner can include a Gold coating over anothermaterial.

The inventive tubing provides a metallic inner layer for optimal airtransport properties as well as flexibility to facilitate installationwithin a building. Because of its flexibility, the cost of installingthe inventive tubing can be significantly less than that of prior arttubing, such as rigid stainless steel tube. One factor affecting theflexibility of the tubing structure is the flexure modulus of thematerial(s) from which the tubing is made. It is well known that for agiven geometry, a structure, such as a tube, becomes more flexible whenmade with materials having a low flexure modulus. As used herein,flexibility refers to the amount by which the tube will deflect as it issubject to a bending force.

FIG. 2A shows how the inventive tubing will bend when suspended betweentwo is points separated by a distance L and a force F is applied for atubing having an outer diameter D and an inner diameter d. For a givengeometry (fixed values of L, D, and d) and the application of apredetermined force F, the amount of deflection Z (the tubing'sflexibility) increases as the flexure modulus of the tubing material isdecreased, Because the flexure modulus for 304 stainless steel isrelatively high (approximately 28×10⁶ PSI, as opposed to about 0.5×10⁶PSI for a relatively stiff PVC material that might be used in the tubingjacket), the application of some predetermined amount of force F onstainless steel tubing will deflect significantly less than the sametubing configuration made from a plastic material, for example. Becauseof the differences in flexure modulus, depending on the thickness of themetallized liner, the inventive tubing, which includes a non-metallicouter jacket, will be 50 to 100 times (or more) flexible than 304stainless steel tubing. That is, the effective flexure modulus of thecomposite tubing (inner metallic layer and outer jacket) isapproximately 50 to 100 times less than that of 304 stainless steeltubing. It is understood that this lesser flexure modulus as compared to304 stainless steel tubing is applicable to the various exemplaryinventive tubing embodiments shown and described herein.

FIG. 3 shows an exemplary embodiment of a composite tubing 300 inaccordance with the present invention having a metallic material 302applied to the inner surface of a tubing material substrate 304. Themetallic material 302, which forms a liner for the tubing 300, may be ametallic paint, a deposited metal (utilizing any one of various knownmetal deposition techniques) or, a metallic insert or metal tube slippedinto the substrate 304.

In one embodiment, the coating 302 on the inner surface of the substrate304 can be applied by slitting a prefabricated length of tubing (e.g.polyethylene) along one radius, opening the tube to expose the innersurface, and applying a thin metallic film (such as stainless steel) bythe vacuum vapor deposition technique. The tubing 300 is then resealedby ultrasonic welding providing, for example, a polyethylene or PVC tubewith a thin-film stainless steel lining.

This tubing fabrication process yields an inner surface coating 302 thatis more uniform than the liner surface of FIG. 2 and eliminates seamsthat can affect particle transport efficiency.

In another embodiment, instead of substrate 304 being a prefabricatedlength of tube, substrate 304 may be an extruded ribbon of jacketmaterial, that is metallized to form coating 302. The metallizedsubstrate is then rolled to form a tube 300 and its seam is sealed usingultrasonic welding techniques.

In another embodiment, a composite tubing is fabricated by applying ametal film as a polyethylene or PVC tubing is extruded. A relativelysmall metal vaporization probe is located near the extrusion dieapplying vaporized metal, such as stainless steel, to the inner surfaceof the tubing at it passes through the forming guides while maintaininga vacuum in the working area.

In another embodiment shown in FIG. 3A, a tubing 300 includes a liner302 formed from a material such as Mylar®, Teflon®, Kapton®, or someother suitable film, which is coated with metal, and adhered to theouter jacket 304 by way of a copolymer adhesive placed between the liner302 and the outer jacket 304.

FIG. 3B shows an exaggerated cross sectional unfolded view of thecomposite liner 302 of FIG. 3A including a substrate 306 that is, usingvapor deposition, sputtering, or other similar techniques of metaldeposition known to those skilled in the art, deposited with a metalliclayer 305 that comprises stainless steel. Alternatively, the metalliclayer can be made of other materials such as gold, brass, or othersuitable conductive materials that yield relatively good chemicalinertness and low absorptive and adsorptive qualities. The liner 302 canalso include a co-polymer adhesive (such as a thermo-set adhesive) 307that is used to adhere the liner to the outer jacket 304 (FIG. 3A)during the extrusion process.

One advantage of using the liner 302 shown in FIG. 3B is that the tubecan be lined using a relatively simple manufacturing process, which canbe similar to the process to create the assembly of FIG. 2, in which themetallic liner is formed into a tube over a forming die and a suitableplastic material such as polyethylene or PVC is extruded over it. Incases where the composite tubing described in this invention is intendedfor use in environments requiring a stringent smoke and flame rating,such as plenum and riser environments described by the NationalElectrical Code, it is undesirable to use polyethylene in the outerjacket (204 & 304) due to the exorbitant smoke that is generated by mostkinds of polyethylene materials when they burn. As an alternative, oneof any number of flame retardant PVC materials may be used for thispurpose and in doing so, the assembly can be certified under the moststringent of tests, such as NFPA 262 or UL910, which is used to qualifycables for use in plenum environments. Using PVCs also results in atubing arrangement that is less stiff or more flexible, which is adesirable property as this makes such tubing easier to install in abuilding environment, particularly as it is incorporated to form astructured cable such as that depicted in FIG. 6.

One consideration in using a softer more flexible material such as PVCover polyethylene is that it provides less retention capabilities toprotect the inner liner 202 (FIG. 2) or 302 (FIG. 3A, 3B) frompermanently deforming should the assembly be subject to crushing orexcessive bending. One factor which results in permanent deformation ofthe inner liner when subject to these conditions is the thickness of theliner's metallic layer. Thus, when constructing the outer jacket of PVC,it is desirable to make the metal layer as thin as possible, and thismakes the composite liner 302 of FIG. 3B highly suitable, as thismetallized layer can be made very thin, using vapor deposition orsimilar techniques. For example a common maximum deposition thicknessfrom vapor deposition techniques is 2000 Å, which is approximately 250times thinner than available stainless steel foil, such as that whichmight be used for liner 202. As a result, a composite tube utilizing thecomposite liner depicted in FIG. 3B will be highly flexible and crushresistant. Additionally, a deposition thickness of 5000 Å or more ispossible using more various techniques. Having a surface coating with athickness of this magnitude may be desirable to promote betterconductivity and abrasion resistance. Conversely, depending on thesputtering process used, a deposition thickness of 200 Å or less may besufficient to provide sufficient performance against adsorption andabsorption of constituents within air samples, while also providing anacceptable level of conductivity to promote good particle transportefficiency.

For example, where the liner 302 of FIG. 3B is utilized, the substrate306 is made of 0.001 inch thick Mylar® and 1000 Å of stainless steel isdeposited on its surface. Mylar is a preferred material for thesubstrate 306 because it is strong and tear resistant, which isadvantageous for the extrusion process, in which the substrate issubject to large forces as it is pulled through the extrusion head. Inaddition, in this configuration, due to the very good performance of thethin metallized surface 305 to spring back to its original shape, thetubing can be made with a relatively large inner diameter (ID) whilestill being highly crush resistant and resistant to kinking and othersources of permanent deformation, For example, in an exemplaryembodiment where the outer diameter (ID) is ⅜ of an inch using the innerlining of FIG. 3B, the tube can be constructed with an ID of 0.310inches. Such a large ID is desirable as it results in less restrictionto airflow, compared to tat of a smaller ID, as air samples are drawn bythe system, thus reducing pressure drop in a system for a given flowrate. This helps to reduce pump capacity issues as well as to promotebetter particle transport efficiency on air samples taken by the system.The reason for the latter is that air sampling systems, such as thatdescribed in U.S. Pat. No. 6,125,710 tend to operate at relatively highflow rates (typically 20 liters per minute or more). At these flowrates, several PSI of pressure drop can be realized in a system, dueprimarily to frictional losses along the length of the tube. Pressuredrops of this magnitude have a large impact on the density of theflowing gas (air), resulting in variations in the velocity of the gas asit travels along the length of the tube. This change in velocity oracceleration has a tendency to cause particles to drop out of the flowstream, and are therefore lost from the sample, as a result of theinertial affects due to particle mass.

FIG. 4 shows an exemplary composite tubing 400 in which a suitable hostmaterial 402 is impregnated with a metallic material 404. The tubing 400can be provided in various embodiments having uniform and non-uniformdistribution of metallic material along the cross section of the tubing.

In one particular embodiment, the tubing 400 includes finely dividedstainless steel flakes with polyethylene, mixed immediately before theextrusion process. The quantity of stainless steel should be sufficientto provide occlusion of the inner surface of the tube to any significantamount of polyethylene on the exposed surface. The stainless steelflakes can range in size from several tens of microns down to a fractionof a micron in size. This variation has the working properties ofpolyethylene tubing with nearly the same chemical inertness as stainlesssteel tubing while also providing an electrically conductive innersurface that inhibits electrical charge from collecting on the innersurface as air samples are drawn to promote efficient particletransport.

In another embodiment, the host material 402 is Teflon® and the metallicmaterial 404 is finely divided stainless steel. This combination canyield an inner surface that has lower absorption and out-gassingproperties than stainless steel impregnated polyethylene. Teflon® hasinherently low absorption and out-gassing properties allowing theformation of tubing using a process that is less dependent on theability to control the packing density of the metallic material.Variations in the packing density of the metallic material can cause theinner surface area of the tubing to take the undesirable properties ofthe polyethylene where the packing density is relatively low.

FIGS. 5A and 5B show another exemplary embodiment of a composite tubing500 in accordance with the present invention having an inner surface 502formed in part from a nonmetallic material 504 and in part from ametallic material 506. The tubing 500 includes metallic strips 506imbedded in the surface of the nonmetallic material 504.

In one particular embodiment, the metallic material 506 that forms theinner surface of the tubing 500 is substantially flush with the surfaceof the nonmetallic material 504. The metallic material 506 provides aconductive path to dissipate electrical charge that is transported as aresult of airflow through the tubing to promote efficient transport ofparticulate matter through the tubing for air sampling purposes.

Gaps 508 between the conductive metallic material 506 should besufficiently small so as to ensure that only a negligible electric fieldcan be established between conductors as a result of the air flow ratethat is applied through the tubing for a given sampling application. Inone embodiment the metallic material 506 includes stainless steel andthe nonmetallic material 504 includes Teflon®.

FIG. 6A is a cross-sectional view of an exemplary embodiment of astructured assembly 600 including a composite tubing 650 and variousgroups of conductors that can be used within an air sampling system inwhich the assembly may be installed. FIG. 6B is an isometric view of thestructured assembly 600 of FIG. 6A. The groups of conductors, which canbe helically wound around the tubing 650, can provide power,communications, and various signals that may be monitored within asystem. The structured assembly 600 simplifies and lowers the cost ofthe installation of the power and communications cables (as well as thetubing) provided with such systems.

The exemplary structured assembly 600 is well suited for use in an airsampling system, such as the illustrative air sampling system 700 ofFIG. 7. The system 700 can be installed in a building and can form apart of a building control system having controllers distributedthroughout a building communicating over one common network. The system700 can include a sensor suite and controller 702, which can be remotelylocated, coupled to one or more node controller modules 704 a,b.Termination points 706 can be located in various rooms to take airsamples that are passed to the sensor suite 702 via the node controller704 a The node controllers 704 a,b can be networked together andcontrolled over a network by the central controller 702. Each nodecontroller 704 controls a valve that is dedicated to each room fromwhich an air sample is to be taken. The termination points 706, nodecontroller 704, and sensor suite 702 can be connected via the structuredassembly 600 of FIG. 6, for example.

Air samples are taken from each room in the system in a multiplexedfashion and brought back to the sensor suite 702. In addition, discretesensors (such as for temperature and relative humidity) may be disposedwithin the termination point locations shown for each room and the dataassociated with each may be sampled by each node controller, either byway of a serial connection to each termination point or by connectinganalog and/or digital signals between the termination point and the nodecontroller. Further details of an exemplary air sampling system arediscussed in U.S. Pat. No. 6,125,710.

Referring again to FIG. 6, the assembly 600 includes a composite tubing650 having a metallic layer 652 and a tubing jacket 654. In a region 602between a cable jacket 604 and the tubing jacket 654, various cables andwires are disposed. In an exemplary embodiment, the assembly 600includes first, second, third, and fourth cable structures 606, 607,608, and 609. Cable structures 606, 607, and 608 are used to provide acombination of power, signal and communication connections for thesystem.

The fourth cable structure 609 is used to provide a dedicated sensingfunction, which helps to optimize the performance of the system 700.Additionally, the assembly 600 includes a ripcord 610 to aid with theremoval of the outer jacket 604 during field installation of the cable.Ripcords are a common feature to structured cable assemblies. Forexample, many of the cables in the composite cable line (for example,Belden 7876A composite data, audio, video, security, and control cable)offered by Belden CDT Inc., a major wire and cable manufacturer, includeripcords.

In one particular embodiment, the first cable structure 606 includes a22 AWG twisted pair to carry signals and the third cable structure 608includes a 22AWG TSP having a drain wire 608 a and foil shield 608 b toprovide communications for some connections and signals for others. Thesecond cable structure 607 includes an 18 AWG triad-type stranded cableto carry power for the system components.

The function served by cable structures 606, 607, and 608 variesdepending on which portion of system 700 (FIG. 7) the cable 600 is usedin. For example, when making connections between node controllers 704a,b or 702, (FIG. 7) the second cable structure 607 will typically beused to provide power from a power supply (residing within or inproximity to the Sensor Suite 702) to the various Node Controllers inthe system. For the system 700 this will typically be 24VAC power andground, however, different embodiments of this system can be made tooperate off of other power sources (for example +/−15VDC and ground)that would likewise be supplied through cable structure 607. Whenconnecting between node controllers 704, or a node controller 704 andthe Sensor Suite 702 the third cable structure 608 serves as the networkcable over which the node controllers 704 and the sensor suite andcentral controller 702 communicate. For these connections, in anexemplary embodiment of system 700 the third cable structure 608 formsthe backbone of a data communications network having an EIA485 (orequivalent) physical layer. It should be obvious to those skilled in theart of data network design that networks of this type often utilize atwisted-shielded pair of conductors with a drain wire, as has beenspecified for the third cable structure 608, in order to both constrainthe characteristic impedance of the cable and to provide a degree ofnoise immunity to the network. Further, when the structured cable 600 isused to make connections between node controllers 704 or between nodecontroller 704 a and the sensor suite 702, the first cable structure 606will typically not be utilized, or will serve some ancillary andnon-predetermined purpose that may arise in custom applications ofsystem 700.

When making connections between a node controller 704 and a terminationpoint 706, the second cable structure 607 will typically be used toprovide power and signal ground to the discreet sensor devices andinstrumentation that resides at the termination point 706. Additionally,when connecting to termination point 706, the first and second cablestructures 606, 608 may be used to connect the signal outputs from thevarious sensors located within 706 to the node controller 704 whichsamples these signals and communicates them back to central controller702. Examples of the sensor types that may exist at 706 includetemperature, relative humidity, and ozone sensors.

The fourth cable structure 609 provides sense lines to optimize thetiming sequence for air samples. In one particular embodiment, the senselines are provided as 26 AWG twisted pair wires. The sense lines 609 areused to measure the distance between the sensor suite 702 of FIG. 7 andeach termination point 706 within the system, in order to estimate thetransport time of each air sample from each location to the sensorsuite. The flow rate, and therefore transport velocity will usually beregulated at the sensor suite 702. Therefore the sample transport timefor each of the sensed locations may be computed by dividing theestimated distance by the same velocity. This is helpful in optimizingthe sampling rate of the system, because in larger systems the transportdistance may be a few hundred feet, resulting in appreciable transporttimes. For example, at a flow velocity of twenty feet per second, asample taken over four hundred feet has a transport time of twentyseconds.

In addition to estimating transport time, measuring transport distancecan be advantageous when the sensor suite 702 is used to performparticle measurements. Even though the transport efficiency ofparticulates is good through the inventive tubing, particle loss forlarger particles (e.g., greater then 1 uM) may vary significantly withtransport distance, especially when samples are taken over a distance ofseveral hundred feet of tubing. However, the percentage loss is fairlypredictable with distance at a given flow rate and thus, knowledge ofthe transport distance provides a way to compensate for this loss.

FIG. 8 is a schematic view 800 of the electrical circuits created by thesense lines 801 as they are distributed by way of a structured cable 600throughout the system 700 depicted by FIG. 7. Termination points 806therefore correspond with 706 in system 700 and node controllers 804correlate with node controllers 704. The line length measurement device802 is typically housed within the sensor suite and central controller702 or in close proximity (typically within 40 feet) to 702. As shown inFIG. 8, and as has been illustrated in FIG. 6, the sense lines arepreferably a pair of wire conductors 801 a,b. This conductor pair isdistributed through system 700/800 where it is connected to the variousnode controllers 804, termination points 806, and to a line lengthmeasuring device 802. Each of the node controllers 804 contain a numberof pairs of electrical switches 803, which are used to selectivelycomplete a circuit between the line length measurement device 802 andthe individual termination points 806 in order to measure the distancebetween the termination point 806 and the line length measurement device802. Techniques for making the distance measurement are dependant onphysical properties of the conductor pair 801 a,b that vary withconductor length. For example, in one embodiment the distancemeasurement is based upon the measurement of the total ohmic resistanceof the conductor pair 801 a,b between the line length measurement deviceand a given termination point 806, as measured between 802 a and 802 b.It should be obvious to those skilled in the art of electronics thatthere are a great variety of circuits that can be designed to make sucha measurement. For example, in one embodiment a current source may beapplied as an electronic circuit component within line length measuringdevice 802 to generate a precise electrical current that can be made toflow out of point 802 a, through the sense line 801 a down to thespliced connection 805 and back through 802 b. Spliced connection 805could be made by twisting the ends of the conductor pairs 801 a,btogether at termination point 806, or connecting 801 a,b together usinga wire nut, or any other suitable means used to join two electricalconductors together. The resultant voltage between points 802 a and 802b is simultaneously measured by a separate circuit within 802, whichsignal is proportional to the resistance between 802 a and 802 b, whichis proportional to the distance to the termination point. When using amethod such as this, sense lines 801 a,b are connected together to forma splice connection 805 at each termination point 806 and the totalresistance of the circuit (formed by the conductors in 801 a and 801 b,the closed switch 803, and spliced connection 805) is measured by themeasurement device 802.

As a further example, using this resistance measurement method, in orderto measure the distance between termination point 806 a and the linelength measurement device 802, the switch pair 803 a in node controller804 a would be closed while keeping all other switches 803 in the system800 open and the resistance of the resultant circuit between 802 a and802 b is measured. Note that the actual length of the circuit is twicethe actual distance being measured because of the combined lengths ofboth conductors 802 a and 802 b. This helps to enhance the resolution ofsuch a measurement system while minimizing the magnitude of the currentthat must be sourced from line measurement device 802.

In an exemplary embodiment, the sense lines 801 are a 26AWG solidtwisted pair of copper wire that can be, for example Beldon Equivalent9976, which has a resistance specification of 40.81 ohms per thousandfeet. Alternatively, wire of finer or coarser gage and using differentconfigurations, such as stranded wire, and made of different materials,such as aluminum or other materials may be used. However, the materialof choice should have a relatively low temperature coefficient ofresistivity to ensure the accuracy of the measurement is relativelyinsensitive to temperature because temperature may vary dramaticallythroughout a given building through which cable assembly 600 isinstalled.

Resistance varies with temperature according to Equation 1 below:R _(T) =R ₂₀[1+α(T−20)]  (Eq. 1)

where,

R_(T)=Resistance in ohms at actual temperature

R₂₀=Resistance in ohms at 20° C.

α=temperature coefficient of resistivity

T =Actual temperature in ° C.

In a typical commercial building environment, including common areas,rooms, interstitial spaces, and penthouses the typical operatingtemperature range the cable assembly 600 will be exposed to is 0 to 40°C. As was previously stated, in the preferred embodiment of thisinvention, the sense lines 801 will be made of copper. For copper,α=0.00393° C.⁻¹which, based on Eq. 1 means the tolerance due totemperature on distance measurements based on resistance with copper isapproximately +/−8%, assuming a standard temperature of 20° C. and anoperating temperature range of 0 to 40° C. This level of accuracy issufficient for most systems 800 where the transport distance is 500 feetor less.

In another embodiment line length measurement device 802 may incorporatea time domain reflectometer (TDR) to measure the distance between atermination point 806 and device 802. Such an approach is based uponapplying a high bandwidth electrical pulse in either a differential orsingle-ended manner to lines 801 a and 801 b and measuring the elapsedtime it takes for the pulse(s) to propagate down the line 801 throughthe selected switch 803 to the termination point 806 and back again.Using a TDR to measure the length of a cable is a well-establishedpractice.

It should be noted that to ensure that the distance measurementperformed using the sense lines is reasonably representative of theactual tube length, the ratio of the length of these conductors to thatof the tube should be controlled. This is one feature of the structuredcable assembly, as it aids the performance of the air transport tubing.

The exemplary embodiments disclosed herein having metal-lined tubingprovide enhanced particle transport efficiency performance compared toknown tubing made with materials that are highly non-conductive. This isdue to the conductive properties of the metallized liner, which tends tominimize deposition due to electrostatic effects, as discussed. However,another source of particle loss, a mechanism known as thermophoresis,can also have a noticeable impact on transport efficiency.Thermophoresis refers to the migration of particles as a result offorces due to a temperature gradient, where the net force on a particleis in the direction of the region of lower temperature This can be afactor affecting particle transport where the structured assembly 600 isinstalled in a building where large temperature gradients exist betweenthe termination point 706 and various areas within the building overwhich the assembly 600 is routed. For example, the cable assembly 600may be routed through a penthouse or interstitial space that may attimes (during winter months, for example) be at a temperature that issubstantially lower than that of the room (termination point 706) fromwhich air samples are drawn. For example, it is known that thedeposition rate of 0.5 um particles on a surface could be reduced by tenfold by maintaining a temperature difference of 10° C. between adeposition surface and the air that the particles are suspended in.Thermophoretic forces tend to be inversely related to particle diameterand will be most pronounced with particles that are 1 um in size andsmaller.

In another aspect of the invention, a structured assembly 600compensates for thermophoretic forces, as well as providing some degreeof countermeasure for other deposition forces, such as gravitationaleffects and coulombic forces (electrostatic effects) affecting particletransport. This may be accomplished by disposing a heat source along thelength of the composite tubing 650 that is sufficient to maintain theaverage temperature of the inner liner 652 above the temperature of theair sample that regularly passes through the tube 650.

Additionally, another reason for heating the tubing is to preventcondensation of certain VOC's or other gases, including water, thatcould condense out of the air while they are being transported to thesensor suite through the tubing.

In one particular embodiment shown in FIG. 9 the assembly 600 of FIG.6is modified to form the assembly 900 by adding one or more heaterelements 901 to the structured cable assembly. Heater element 901 may beone or more resistive heating elements, made of materials such asnichrome, tungsten, nickel, stainless steel, or other material suitablefor rendering a heater function through which an electrical current canflow, resulting in power dissipation and a temperature rise along thelength of the conductor. This conductor may have a cross section that iseither circular or flat so that the conductor is ribbon shaped.

In the illustrated embodiment, the heater element 901 is made of 28AWGtungsten wire. The source of this electrical current is contained as aseparate electronic module that is part of the sensor suite 702 (FIG.7), from which the average temperature of heater element 901 may becontrolled by either applying a predetermined electrical current to themedium based on the total length of cable 900 or if the material'stemperature coefficient is relatively large, such as that with tungstenor nickel, as an alternate embodiment, the temperature of the heaterelement 901 may be precisely controlled using well established methodsfor controlling the temperature of a temperature-dependant resistivematerial such as, for example, techniques that have been developed forcontrolling the temperature of a hot wire anemometer. See, for example,U.S. Pat. No. 4,523,461.

In one particular embodiment, however, where tungsten is used, aconstant current is applied to the medium. Generally, a heater elementwould most typically be utilized within assembly 600/900 as it connectsbetween Node Controllers 704 (for example between 704 a and 704 b) shownin FIG. 7, as these connections typically involve the longest lengths ofassembly 600 as it is routed through the structure of a building,sometimes over a distance of several hundred feet. However, there aremany cases where a heater element could advantageously be applied withinassembly 600/900 as well as between Node Controllers 704 and theirrespective termination points 706, as large temperature gradients canoften be realized between these connection points within a building andthis can significantly contribute to particle loss.

Another factor that influences particle transport through a tube, is theability of the inner surface of the tubing medium to establish anelectrical charge. As an electrical charge becomes established upon asurface, particulate matter that is suspended above is that surface willhave a tendency to be attracted to the surface if the charge on thesurface and the charge on the particle are opposite in polarity. One ofthe advantages of the conductive liner 652 described herein is itsability to disperse charge, therefore resulting in a relatively lowcharge per unit area compared to that of a poorly conductive surface. Insome cases, however, it may be advantageous to provide an addedconductive path through which charge may flow from the conductive liner652 to some other electrically conductive medium to substantially reducethe amount by which a charge can develop over the surface of conduciveliner 652. As an example, the conductive liner may be electricallyconnected to an electrical ground within a building, or it may beconnected to the frame of a building, or some other component of abuilding that either offers a low impedance path to ground or anothermedium through which the charge can be dispersed over. The conductivepath for charge to flow from liner 652 may be established using anynumber of techniques involving providing either a single connection toground or multiple connections to ground throughout a system.

FIG. 10A is a schematic view 1000 of the distribution of tubing 650distributed by way of structured cable 600 throughout the system 700depicted by FIG. 7. The tubing 650 (also labeled as 1001 in FIG. 10A) isdistributed through system 700/1000 where it is connected to variousvalves 1003 contained within node controllers 1004, and it is connectedbetween valves 1003 and termination points 1006. Also shown is anoptional grounding connection 1010, which may be utilized toelectrically connect the inner liner 652 to a ground within the buildingin which system 1000 is installed, thus providing a path for charge toflow out of system 1000.

In one embodiment, the conductive inner liner 652 of the varioussections of tubing 650 shown in system 700/1000 are electricallyconnected together so that any amount of charge that is applied to anyof the tubing section 1001 a,b,c,d,e,f,g,h,i is equally dispersedthroughout tubing section 1001 a,b,c,d,e,f,g,h,i. These electricalconnections may, for example, be made by using electrically conductivebarbed fittings at valves 1003 and provide a means to electricallyconnect a fitting on one side of the valve 1003 to a fitting on theother side of the valve 1003.

FIG. 10B depicts the way tubing is joined to a valve 1003 within a nodecontroller 1004 using this method, involving barbed fittings 1007 a,bconnecting to each side of valve 1003. Barbed fittings, which are wellknown to those experienced with pneumatic systems, are commonly usedwith most types of flexible tubing and are used to make connections bypushing the tubing over the barb section of the fitting. (Generalexamples of a barbed fittings include those of the Thermobarb® productline by NewAge Industries, Inc.) By making such a connection with tubing1001, each fitting is in contact with the conductive inner liner 652 ofthe tube 1001. For the purposes of this invention, the fitting 1007 maybe made of or coated with any type of conductive material including:metals (such as, for example, brass, bronze, iron, steel, stainlesssteel, and aluminum), conductive plastics, conductive compositematerials, or conductive paint. Further, in one embodiment, valve 1003may itself be made of a conductive material such as, for example,stainless steel or some other metal and thus, when connected to fittings1007 and tubing 1001 as shown provides an electrically continuous pathfor charge to flow between tubing sections 1001 a and 1001 b.

In an alternate embodiment, as shown in FIG. 10C, if valve 1003 is madeof a nonconductive material a shorting strap 1009, connected toterminals 1008 a of fitting 1007 a and 1008 b of fitting 1007 b, may beprovided to electrically connect the inner liners 652 of tubing 1001 a,btogether. Such a conductive strap 1009 may be a copper wire, or a wiremade of some other conductive material that is suitable for thispurpose. The terminals 1008 a,b may be screw-down type clamps capable offastening a wire, such as strap 1009 to fitting 1007, and it may also beused to secure the optional ground connection 1010. Additionally,optional ground 1010 may be provided at one or multiple locationsthroughout system 1000.

In a further embodiment, instead of using barbed fittings 1008, aconductive path is provided for transferring charge from conductiveinner liner 652 through the jacket 654 of tubing 650 by constructing thejacket 654 using a material that is conductive. For example, jacket 654could be made from a composite of plastic that has been impregnated withfinely divided metal flakes, such as that used in tubing 400. Jacket 654can also be made from a plastic resin that has been embedded with carbonpowder or fiber or any number of other conductive filler compositions.

FIG. 11 depicts an exemplary embodiment where the tubing 650 isadditionally wrapped with a conductive shield 1101 and a conductivedrain wire 1102 is disposed between conductive shield 1101 and theconductive tubing jacket 654 to form a low impedance connection betweenthese three elements (654, 1101, and 1102). Conductive shield 1101 maybe composed of metallic foil, such as aluminum foil, analuminum-polyester-aluminum laminate (such as that which is common tomost commercially available shielded cables), or any other suitableconductive material. Likewise, drain wire 1102 may be a conductive wiresuch as the copper drain wire typically found in shielded cables.However, the drain wire 1102 may be composed of other suitableconductive materials as well.

The drain wire 1102 may be connected to ground connection 1010 of system1000 in order to provide a conductive pat for charge to flow fromconductive inner liner 652 to tubing jacket 654, to the conductive outermaterial or shield 1101, and then ultimately through drain wire 1102 toground. When applying cable assembly 1100 to system 1000 tubing andmaking only one ground connection the conductive inner liner 652 betweensections 1001 a,b,c,d,e,f,g,h,i may be electrically connected togetherby splicing drain wires 1102 from each section 1001 a,b,c,d,e,f,g,h,itogether. As is the case for the embodiment with barded fittings, theembodiment using cable assembly 1100 may also be grounded at multiplelocations throughout system 1000. When doing so, it is generally notnecessary to splice the drain wires 1102 from each section 1001a,b,c,d,e,f,g,h,i together.

The interconnection of the conductive inner liner 652 from tubingsections 1001 a,b,c,d,e,f,g,h,i as well as providing an added electricalpath such as ground connection 1010 for charge to flow, are passivemethods to limit charge buildup within a system. Alternatively, however,active methods may be used to either control the electrostatic chargebuildup on inner liner 652 or to control the way in which particlesinteract with the electrostatic charge on surface 652 in order to aid intransporting particles as air samples are taken from various terminationpoints 1006 throughout system 1000.

In one embodiment, air samples that are drawn through tubing 650 insystem 1000 may be exposed to an ionizing source that either positivelyor negatively charges particulate matter drawn from each air sampletaken from termination points 1006. In this embodiment, a voltage isapplied to the conductive inner liner 652 of tubing 650 in order torepel the charged particulate matter from the surface of the conductiveliner 652, thus improving the transport efficiency of particulate matterthrough system 1000. Exemplary ionization sources for ionizable fluidmedia are described, for example, in U.S. Pat. Nos. 6,693,788,4,689,715, 3,711,743, and 3,613,993, all of which are incorporatedherein by reference. More generally, however, ionization devices canutilize any number of electrodes that are exposed to the ionizable fluidmedia (such as air) and are coupled to a high voltage source (typically5K volts or more).

FIG. 12 illustrates an exemplary embodiment 1200 of the application ofan ionization source 1201 applied to the airflow stream in conjunctionwith tubing 650. In this embodiment, a conductive barbed fitting 1205 isbeing used to provide an electrical connection to the conductive innerliner 652 to which a voltage potential may be applied by electricallyconnecting the output of voltage source 1203 to barbed fitting 1205using screw-down clamp 1202. However, other suitable ways of connectingto conductive inner liner 652 may also be used. Here, voltage source1203, which is connected to the same reference 1209 as the ionizingpower source, may either be a DC voltage or a time varying voltagehaving a DC component. The magnitude of this voltage may be any valueranging from several volts to several thousand volts. Voltage source1203 can be considered to be an active device. Because of the potentialhazard that may be created as a result of the potentially large voltagethat may be applied to conductive inner liner 652, voltage source 1203can be designed with energy limiting features by substantially limitingits current sourcing capabilities. Air flow stream 1207 flowing intoionization source 1201 becomes ionized by electrodes 1204 which have alarge voltage potential applied between them from ionization powersource 1206. The resulting ionized flow stream 1208 flows into tubing650 through barbed fitting 1205 and, due to charge established viavoltage source 1203 on conductive inner liner 652, the ionized particleswithin flow stream 1208 will have a tendency to be repelled from thesurface of conductive inner liner 652, resulting in an enhancement toparticle transport throughout tubing 650. For purposes of this inventionan ionization source 1201 may be applied at numerous locationsthroughout system 1000.

While the inventive composite tubing is well suited for use in system700, as described, it is also well suited for use in other types of airmonitoring systems designed to transport air samples and make remotemeasurements of various characteristics of the air with any number ofsensors. For example, the tubing is well suited for use in multi-pointair sampling systems such as that described by U.S. Pat. No. 6,241,950,which is incorporated herein by reference.

In such systems, both the sensor for making air parameter measurementsand the air intake valves for switching samples from locations monitoredby the system are placed in a common location within the building, andthey are typically placed within a common enclosure. FIG. 13 is ageneralized view of such a system, which has a plurality of input portsconnected via tubes 1301 to each room termination point 1308 ofinterest. The termination point 1308 may simply be the location that theend of each segment of tubing 1301 is placed, or it may incorporateother sensors and hardware, such as is the case with system 700. Most ofthe components for this sampling system are contained within enclosure1307, which houses the air intake valves 1302 through which samples aretaken, a means for interconnecting the valves via one common manifold1303, a sensor suite 1304 comprising one or more sensors, a centralvacuum pump system 1306, and a controller 1305.

The system works by sequencing air samples through air intake valves1302 which air samples are thereby drawn through sensor suite 1304 viathe negative pressure established by pump 1306. As an air sample from agiven room or location passes through sensor suite 1304 air parameterssensed by 1304 are monitored and typically recorded by controller 1305.Controller 1305 is also responsible for sequencing air intake valves1302. Many types of tubing 1301 have been used in systems like 1300,including tubing made from polyethylene, Plexco®, Teflon, rigidstainless steel pipe, and other materials. However, the benefitsrealized by system 700 by using inventive tubing, e.g., 200,300,400,500equally apply to systems such as 1300, as well as other multipoint airsampling strategies.

The inventive tubing, e.g., 200,300,400,500 in system 1300, for example,provides a flexible, easy to install, and low cost tubing with goodparticulate transport properties along with low adsorption andabsorption properties. The tubing, e.g., 200,300,400,500 enables thesystem 1300 to remotely monitor low-level concentrations of volatileorganic compounds, while also simultaneously providing capabilities toremotely monitor particulates at locations throughout the buildingwithin which system 1300 is installed. Using the inventive tubing in thesystem 1300 would, for example, enable the use of a photoionizationdetector (for ppb-level VOC monitoring) and a particle counter withinsensor suite 1304.

In addition, air monitoring systems, such as system 1300, can alsobenefit from the structured assemblies 600,900, and 1100 to providepower and communications, along with signal connections to discretedevices and sensors that may be located within various rooms and othermonitoring locations throughout system 1300. This provides a convenientway to expand the capabilities of systems like 1300, while minimizinginstallation costs. Using such assemblies 600,900, and 1100 also enablesdistance measurements to be made using sense lines 609 in order tooptimize the sequencing of air samples from various rooms and othermonitoring locations throughout system 1300. System 1300 may alsoutilize heater element 901 to improve particle transport efficiency andto help prevent condensation of certain VOC's or other gases, includingwater that could condense out of the air while they are beingtransported from the rooms and other locations in system 1300 to thesensor suite 1304. Also, the principles that were described for activelyor passively controlling charge on the tubing's inner liner 652 insystem 700/1000 in order to promote particle transport in air samples,applies to systems such as 1300 as well.

The present invention provides a tubing structure that is well suited totransport “packets” of air in an air sampling system. The tubingincludes a metallic inner layer and an optional outer jacket thatprovides efficient transport of particulate matter through the tubingand relatively little absorption and off-gassing for many air componentsof interest.

One skilled in the art will appreciate further features and advantagesof the invention based on the above-described embodiments. Accordingly,the invention is not to be limited by what has been particularly shownand described, except as indicated by the appended claims, Allpublications and references cited herein are expressly incorporatedherein by reference in their entirety.

1. An air sampling system, at least partially comprising: a sensorsuite; air intake valves for switching air samples; and tubing coupledto the air intake valves and a series of termination points from whichair samples are obtained and transported via the tubing to the sensorsuite, wherein at least a portion of the tubing includes a metallicinner layer surrounded by an outer jacket that is at least partiallyformed of a non-metallic material.
 2. The system according to claim 1,wherein the metallic inner layer includes stainless steel.
 3. The systemaccording to claim 2, wherein the metallic inner layer includesstainless steel in a thickness ranging from about 0.0005 inch to about0.004 inch.
 4. The system according to claim 3, wherein the stainlesssteel is a foil.
 5. The system according to claim 1, wherein themetallic layer includes stainless steel deposited on a substrate.
 6. Thesystem according to claim 5, wherein the stainless steel has a thicknessranging from about 200 Å to about 5000 Å and the substrate includesMylar®.
 7. The system according to claim 1, wherein the tubing has anouter diameter of about ⅜ of an inch and an inner diameter ranging fromabout ¼ inch to about 5/16 of an inch.
 8. The system according to claim1, wherein the metallic inner layer includes Gold.
 9. The systemaccording to claim 1, wherein the jacket includes one or more ofpolyethylene and polyvinyl chloride.
 10. The system according to claim1, wherein the metallic layer is a metallized plastic with an overlapregion.
 11. The system according to claim 10, wherein the metallizedplastic is Mylar® with stainless steel deposited upon it.
 12. The systemaccording to claim 1, further including securing at least one conductorto provide one or more of signal, power, and communication.
 13. Thesystem according to claim 12, wherein the at least one conductor extendsin a region between the tubing jacket and a cable jacket.
 14. The systemaccording to claim 1, wherein the jacket is composed of a conductiveplastic that establishes a conductive path between the metallic innerlayer and the outer surface of the tube.
 15. The system according toclaim 14, wherein the conductive plastic is a plastic resin impregnatedwith carbon.
 16. The system according to claim 14, further including aconductive drain wire disposed along the length of the tube and is incontact with an outer surface of the tubing.
 17. The system according toclaim 16, wherein the drain wire is electrically grounded.
 18. Thesystem according to claim 16, wherein the tube and drain wire arecovered with a conductive shield.
 19. The system according to claim 16,wherein segments of tubing are electrically interconnected by connectingthe conductive drain wire from each segment together.
 20. The systemaccording to claim 1 wherein the metallic inner layer includes segmentselectrically interconnected using conductive barbed fittings.
 21. Thesystem according to claim 1, wherein the metallic inner layer iselectrically grounded.
 22. The system according to claim 1, whereinelectrostatic charge on the surface of the metallic inner liner isactively controlled.
 23. The system according to claim 1, wherein avoltage potential is applied to the metallic inner liner.
 24. The systemaccording to claim 1, wherein airborne particulate matter sampled by thesystem is ionized at one or more locations throughout the system. 25.The system according to claim 1, wherein airborne particulate mattersampled by the system is ionized at one or more locations throughout thesystem and a voltage potential is applied to the metallic inner liner.26. The system according to claim 1, further including providing aconductive medium disposed along a length of the tubing for coupling toa line length measurement device.
 27. The system according to claim 1,further including providing a heat source disposed along the length ofthe tubing.
 28. The system according to claim 27, wherein the heatsource is a resistive wire with a current flowing through it.
 29. Thesystem according to claim 1, wherein the tubing has an effective flexuremodulus that is between 50 and 100 times less than that of 304 stainlesssteel tubing.